Ovary of the pipefish,Syngnathus scovelli

Female ornamentation and the fecundity trade-off in a sex-role reversed pipefish

Sexual ornaments found only in females are a rare occurrence in nature. One explanation for this is that female ornaments are costly to produce and maintain and, therefore, females must trade-off resources related to reproduction to promote ornament expression. Here, we investigate whether a trade-off exists between female ornamentation and fecundity in the sex-role reversed, wide-bodied pipefish, Stigmatopora nigra. We measured two components of the disk-shaped, ventral-striped female ornament, body width, and stripe thickness. After controlling for the influence of body size, we found no evidence of a cost of belly width or stripe thickness on female fecundity. Rather, females that have larger ornaments have higher fecundity and thus accurately advertise their reproductive value to males without incurring a cost to fecundity. We also investigated the relationship between female body size and egg size and found that larger females suffer a slight decrease in egg size and fecundity, although this decrease was independent of female ornamentation. More broadly, considered in light of similar findings in other taxa, lack of an apparent fecundity cost of ornamentation in female pipefish underscores the need to revisit theoretical assumptions concerning the evolution of female ornamentation.

The ovarian structure and mode of egg production in two polygamous pipefishes: a link to mating pattern

In this study, the ovarian structure and mode of egg production were examined in two pipefishes, the broad-nosed pipefish Syngnathus typhle and the straight-nosed pipefish Nerophis ophidion, which show different types of polygamous mating patterns. Syngnathus typhle showed an ovary with one germinal ridge and asynchronous egg production, corresponding to previous findings in other polygamous Syngnathus pipefishes. In contrast, the ovary of N. ophidion had two germinal ridges and eggs were produced synchronously in groups, similar to what has been observed in monogamous syngnathids. The egg production of N. ophidion, however, is clearly distinguished from that of monogamous syngnathids by the additional egg production after an ovulation. It is suggested that the differences in female mating strategies result from the difference in egg production process and that this is related to the difference in mating pattern between these two polygamous species.

Reproductive endocrinology of Syngnathidae

Few studies have examined the underlying hormonal mechanisms that mediate reproductive cyclicity, male pregnancy and reproductive behaviour in syngnathids. Progress in these areas has been hampered by the small size of most species in the family and a lack of validated techniques for assessing endocrine function. Research on a relatively small number of species has suggested that androgens are likely regulators of spermatogenesis and the development of the male brood pouch prior to pregnancy whereas prolactin and corticosteroids synergistically promote brood pouch function during pregnancy. No evidence supports a reversal of reproductive steroid hormone function in sex-role reversed behaviour, but neuropeptides such as arginine vasotocin or isotocin should be examined for their role in regulating parturition and mating behaviour. The diversity of reproductive patterns exhibited by syngnathids suggests that they will provide a unique opportunity to assess how hormonal regulation of integumentary function, gametogenesis and reproductive behaviour have evolved within a teleost lineage. Additionally, their coastal distribution and embryo retention make them potentially important subjects for studies on the effect of endocrine disruption on fitness.

Quantification of whole brain arginine vasotocin for two Syngnathus pipefishes: elevated concentrations correlated with paternal brooding

Arginine vasotocin (AVT) regulates many aspects of fish physiology and behavior including courtship and reproduction. This study begins to address whether paternal functions for AVT have independently evolved in species in which paternal behavior has evolved. We quantified AVT in the brains of Syngnathus fuscus and Syngnathus floridae which, like other pipefishes and seahorses of the family Syngnathidae, brood embryos within specialized structures of the male. For both species, we measured AVT concentrations seventeenfold higher for some males during brooding compared to post-brooding males. Comparable whole brain AVT concentrations between gravid females and males with broods at some embryonic development stages suggest physiological similarities that we hypothesize is related to nutrient provisioning but should be elucidated with further studies including a detailed anatomical analysis of AVT production. Earlier studies have identified differences in the brooding structures of these species. Here we documented interspecific differences in the variability and mean AVT concentration for non-brooding males, the brood stage showing a return to post-brooding concentrations, and the variability of AVT concentrations for brooding males with embryos in some development stages. Future investigations should use these data to investigate the potential for divergent AVT function between species, sexes, and brooding males with embryos of different developmental stages.

Cooling of pacu (Piaractus mesopotamicus) embryos at various stages of development for 6 or 10 hours

The objective of this research was to verify the effects of cooling embryos of pacu, Piaractus mesopotamicus, in four stages of development during two stocking periods. The stages of embryo development were at: blastoderm, ∼ 64 cells-1.4 h after fertilization (haf); 25% of the epiboly movement--5.2 haf; blastoporous closing--8.0 haf; and optical vesicle appearing--13.3 haf. Embryos were exposed to a cryoprotectant solution containing methanol (10%) and sucrose (0.5 M). Thereafter, embryos were submitted to a cooling curve until they reached -8 °C, and then kept cooled for 6 or 10 h. In addition, for each stage of embryonic development, a control group with uncooled embryos was used to compare hatching rates. The total number of larvae from the first two stages of ontogenetic development (1.4 and 5.2 haf) was lower compared to the other stages (0.0 and 8.0 haf). There was no significant difference between stages 8.0 and 13.3 haf for the total number of larvae (49.9 ± 6.7% and 55.2 ± 6.7%, respectively). Embryo diameter varied according to embryonic stage, providing evidence of differences in membrane permeability. There was a negative correlation between embryo diameter and the total number of larvae (r = -0.372). In conclusion, use of embryonic stages 8.0 and 13.3 haf were recommended for maintaining cooled pacu embryos at -8 °C for 6 or 10 h.

Reproductive compensation in broad-nosed pipefish females

The differential allocation hypothesis assumes that animals should weigh costs and benefits of investing into reproduction with a current mate against the expected quality of future mates, and predicts that they should invest more into reproduction when pairing with a high-quality mate. In the broad-nosed pipefish (Syngnathus typhle), males care for the embryos in a brood pouch and females compete for access to male mating partners. Both sexes prefer mating with large partners. In the present study, we show that the same female provides both large and small mating partners with eggs of similar size, weight and lipid content when mated to two males in succession. Importantly, however, eggs provided to small males (less preferred) had higher egg protein content (11% more) than those provided to large males (preferred). Thus, contrary to the differential allocation hypothesis, eggs did not contain more resources when females mated with a larger male. Instead, the pattern observed in our results is consistent with a compensatory reproductive strategy.

Morphological and histochemical characteristics of the epithelium of ovarian lamellae of Genypterus blacodes (Schneider, 1801)

The physiological significance of the glycoproteins (GPs) secreted by the epithelium of ovarian lamellae is discussed in reference to the reproductive biology of G. blacodes. Histochemical procedures for localising and characterising GPs were used to determine the cytoplasmic components of cells of the epithelium that covers the ovarian lamellae of pink cuskeel, Genypterus blacodes (Schneider, 1801) (Pisces, Ophidiidae), during spawning. This species is one of the most valuable demersal fish resources in the Argentine Sea, mainly due its large size and flesh quality. GPs with oxidizable vicinal diol groups, sialic acid with or without O-acyl substituents, O-acyl sugars, neutral sugars and GPs with carboxyl and sulphate groups were detected. Light microscope examination showed morphological changes in the epithelium of ovarian lamellae during the spawning season, associated with a secretory activity of mucus. Optical density studies revealed the presence of polyploid cells encompassing those morphological changes. Results of the present study suggest that the epithelium of ovarian lamellae of G. blacodes performs a secretory role, which is intensified during ovarian maturity, suggesting that G. blacodes could release masses of eggs enveloped in mucus.

A monogamous pipefish has the same type of ovary as observed in monogamous seahorses

Syngnathid fish (pipefish and seahorses) are unique among teleost fish in that their ovary consists of a rolled sheet with germinal ridge(s) on the dorsal side running along the entire length of the sheet. A distinct difference is seen in the ovarian structure between polygamous Syngnathus pipefish and monogamous seahorses (Hippocampus spp.), the former having one germinal ridge and the latter with two ridges. This study examined the ovarian structure and the mode of egg production in a monogamous pipefish Corythoichthys haematopterus. The ovary of C. haematopterus had two germinal ridges like that observed in monogamous seahorses. There were two distinct groups of follicles in the ovary, one being a cohort of extremely small follicles and the other a cohort of follicles developing and increasing in size with the passage of time. We suggest that the ovarian structure and the mode of egg production in this pipefish are adaptations to monogamy.

Gonadal morphology of the weedy seadragon, Phyllopteryx taeniolatus (Lacépède): characterisation of ovarian and testicular maturation

Because little is known about the reproductive biology of the weedy seadragon, Phyllopteryx taeniolatus, we sought to characterise for the first time the morphology and histology of the gonads of female and male weedy seadragons. Each seadragon ovary consisted of a pair of cylindrical tubes with a total of four tubes per female with follicles arranged with less mature oocytes originating from the germinal ridge and progressively more advanced oocytes occurring in a spiral fashion around the periphery of less-developed oocytes. Seadragon testes had a system of interconnecting seminiferous tubules with spermatocyte development occurring within the tubule. Spermatocytes were observed along the testis wall and appeared to emerge into the lumen where further development of spermatocytes occurred. This study represents the first examination of the gonadal structures of the weedy seadragon, a species currently classified by the International Union for Conservation of Nature (IUCN) as ‘Near Threatened’. The descriptions of morphological development of the gonads may be useful in the histological identification of the stages of gametogenesis and reproductive status of other syngnathids. In addition, this information may also provide useful information in elucidating the phylogeny of this family of fishes.

Germ cells are essential for sexual dimorphism in the medaka gonad

To further elucidate the roles of germ cells in the sex differentiation of gonads, we have used the medaka, a teleost fish, to generate mutants that lack germ cells from the onset of gonadogenesis by the morpholino-mediated knockdown of cxcr4. The resulting germ-cell-deficient medaka show female-to-male sex reversal of their secondary sex characteristics, accompanied by increased levels of androgen and reduced levels of estrogen. A failure to maintain granulosa cells or estrogen-producing cells also occurs at early stages of sex differentiation in the cxcr4 morphants, before the initiation of gonadal morphogenesis. In contrast, androgen-producing cells are unaffected in germ-cell-deficient medaka of either sex. In addition, a single tube-like gonad that expresses male-specific genes is formed in these mutants irrespective of the genetic sex. Significantly, each of these mutant phenotypes occurs in a somatic cell-autonomous manner, suggesting that gonadal somatic cells are predisposed toward male development in the absence of germ cells. This highlights the importance of germ cells in the sexual dimorphism of the gonads.

nanos1 is required to maintain oocyte production in adult zebrafish

Development of the germline requires the specification and survival of primordial germ cells (PGCs) in the embryo as well as the maintenance of gamete production during the reproductive life of the adult. These processes appear to be fundamental to all Metazoans, and some components of the genetic pathway regulating germ cell development and function are evolutionarily conserved. In both vertebrates and invertebrates, nanos-related genes, which encode RNA-binding zinc finger proteins, have been shown to play essential and conserved roles during germ cell formation. In Drosophila, maternally supplied nanos is required for survival of PGCs in the embryo, while in adults, nanos is required for the continued production of oocytes by maintaining germline stem cells self-renewal. In mice and zebrafish, nanos orthologs are required for PGC survival during embryogenesis, but a role in adults has not been explored. We show here that nanos1 in zebrafish is expressed in early stage oocytes in the adult female germline. We have identified a mutation in nanos1 using a reverse genetics method and show that young female nanos mutants contain oocytes, but fail to maintain oocyte production. This progressive loss of fertility in homozygous females is not a phenotype that has been described previously in the zebrafish and underlines the value of a reverse genetics approach in this model system.

Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout,Oncorhynchus mykiss(Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes)

The rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is a salmoniform fish that spawns once per year. Ripe females that had ovulated naturally, and those induced to ovulate using salmon gonadotropin-releasing hormone, were studied to determine whether follicles were forming at the time of spawning and to describe the process of folliculogenesis. After ovulation, the ovaries of postspawned rainbow trout were examined histologically, using the periodic acid-Schiff procedure, to stain basement membranes that subtend the germinal epithelium and to interpret and define the activity of the germinal epithelium. After spawning, the ovary contained a few ripe oocytes that did not ovulate, numerous primary growth oocytes including oocytes with cortical alveoli, and postovulatory follicles. The germinal epithelium was active in postspawned rainbow trout, as determined by the presence of numerous cell nests, composed of oogonia, mitotic oogonia, early diplotene oocytes, and prefollicle cells. Cell nests were separated from the stroma by a basement membrane continuous with that subtending the germinal epithelium. Furthermore, follicles containing primary growth oocytes were connected to the germinal epithelium; the basement membrane surrounding the follicle joined that of the germinal epithelium. After ovulation, the basement membrane of the postovulatory follicle was continuous with that of the germinal epithelium. We observed consistent separation of the follicle, composed of an oocyte and surrounding follicle cells, from the ovarian stroma by a basement membrane. The follicle is derived from the germinal epithelium. As with the germinal epithelium, follicle cells derived from it never contact those of the connective tissue stroma. As with epithelia, they are always separated from connective tissue by a basement membrane.

Differential parental nutrient allocation in two congeneric pipefish species (Syngnathidae:Syngnathusspp.)

Male seahorses and pipefishes of the family Syngnathidae are heralded for their unique brood pouch structures for incubating embryos. There are three general types of brood pouch with increasing complexity: simple ventral gluing, two pouch flaps and a completely sealed sac. The diversity of functional roles within a type in providing nutrition, aeration and protection to offspring is unknown. Here we reveal significant differences in parental nutrient allocation to embryos for two closely related, sympatric pipefishes with similar brood pouch structure. We document differences in embryo attachment, depletion of pouch fluid nutrients over development and egg nutrient partitioning between Syngnathus floridae and Syngnathus fuscus. In S. fuscus, females produce nutritionally poor eggs and the males implant developing embryos in the brood pouch adjacent to blood vessels. A female-biased breeding population was observed, supporting the hypothesis that the cost of male parental care is high in this species. The loose connection between eggs and brood pouch tissues and the appearance of undeveloped eggs and lipid droplets in the pouch of S. floridae males suggest this species utilizes nutrient-rich eggs produced by females as nurse eggs to supplement embryonic development. A balanced sex-ratio for S. floridae further supports more equal parental contribution. This comparison provides evidence of a decline in female gametic investment and reveals the rapid diversification of syngnathid brood pouch function. Our results indicate gross classification of brooding structures into one of the three general pouch types does not predict the energetic investment of males in parental care. But rather, physiological characterization of the relative investment by each sex to offspring is essential to understanding the functional significance of the brood pouch.

Monogamy and sex role reversal in the pipefish Corythoichthys haematopterus

We observed the mating pattern and social behaviour of the pipefish Corythoichthys haematopterus in temperate waters of Japan during three successive breeding seasons. Males cared for a clutch in their brood pouch for 9-19 days until hatching and had several broods in the season with nonbrooding intervals of only 1 or 2 days. The population sex ratio was female biased and some females were always excluded from reproduction. Although males were sometimes courted by unmated females together with their regular partners, they always mated with the latter. The pair bond was maintained until the next season if both members survived. When males lost their partners, they remated with neighbouring unmated females within a few days. In contrast, widowed females remained unmated for a long time. Females had larger home ranges and were more active in courtship displays than males. This pipefish provides the first example of sex role reversal among monogamous syngnathid fish. We suggest that mate guarding by females is a primary proximate factor for maintenance of monogamy in this fish. Copyright 2001 The Association for the Study of Animal Behaviour.

Ultrastructural observations on sperm storage in the ovary of the platyfish, Xiphophorus maculatus (Teleostei: poeciliidae): the role of the duct epithelium

Sperm storage is an important phenomenon occurring in viviparous and oviparous teleosts and contributes to the reproductive life history of these forms. There is a paucity of morphological studies on sperm storage in fishes. The majority of these have been confined to the light level of investigation. In this report, we describe, at the ultrastructural level, sperm storage in the viviparous platyfish, Xiphophorus maculatus. Female platyfish, as is typical of the poeciliids, are capable of storing viable sperm for up to several months within the ovary and gonoduct. We observed that sperm stored within inseminated platyfish became associated with specific epithelial cells (SACs) lining the oviduct. Two forms of association were seen: 1) sperm were found within deep surface pits and pockets, and 2) the spermatozoa were taken up and incorporated within the cytoplasm of the SACs. Junctional complexes in the form of tight junctions (zona occludens) and desmosomes at the apico-lateral surfaces of the SACs were prevalent. The junctions could have contributed to allograft survival of the haploid heterogenetic sperm cells within the female's reproductive tract. Our results shed light on the mechanism of sperm storage in the platyfish and could serve as a model for other poeciliid species and teleosts that are capable of storing sperm.

Ovarian germinal epithelium and folliculogenesis in the common snook, Centropomus undecimalis (Teleostei: centropomidae)

The ovarian germinal epithelium in the common snook, Centropomus undecimalis, is described. It consists of epithelial and prefollicle cells that surround germ cells, either oogonia or oocytes, respectively. The germinal epithelium borders a body cavity, the ovarian lumen, and is supported by a basement membrane that also separates the epithelial compartment of the ovarian lamellae from the stromal compartment. During folliculogenesis, the epithelial cells, whose cytoplasmic processes encompass meiotic oocytes, transform into prefollicle cells, which become follicle cells at the completion of folliculogenesis. The follicle is a derivative of the germinal epithelium and is composed of the oocyte and surrounding follicle cells. It is separated from the encompassing theca by a basement membrane. The cells that form the theca interna are derived from prethecal cells within the extravascular space of the ovarian stroma. The theca externa differentiates from undifferentiated cells within the stromal compartment of the ovary, from within the extravascular space. The theca interna and the theca externa are not considered to be part of the follicle and are derived from a different ovarian compartment than the follicle. Meiosis commences while oocytes are still within the germinal epithelium and proceeds as far as arrested diplotene of the first meiotic prophase. The primary growth phase of oocyte development also begins while oocytes are still within the germinal epithelium or attached to it in a cell nest. The definitions used herein are consistent between sexes and with the mammalian literature.

Reproductive aspects of the gulf pipefish, Syngnathus scovelli (Teleostei: Syngnathidae), from Southeastern Brazil

This study attempts to assess the relationship between fecundity and fertility of males and females of the gulf pipefish, Syngnathus scovelli. Specimens of this pipefish were collected in detached algae in the inner surf-zone of a dissipative sandy beach in southeastern Brazil. 97 specimens were collected, and they were associates to detached algae. From these, 14 were males, 36 females and 47 immature. Male-female sex ratio was 0.4:1, which was significantly different from the expected 1:1 ratio. Fish ranged from 43 to 98 mm TL (Fig. 1), and males and females showed similar size. Only 7 males were pregnants, while 9 females had hydrated oocytes. Minimum number of eggs/embryos in the pouch was 30 and the maximum 92. Minimum number of hydrated oocytes was 36, and the maximum was 165. The number of egg/embryos, and hydrated oocytes were weakly related to total length. It seems that the gulf pipefish occupy the inner surf-zone of the Praia do Iate are brought to the shallows accidentally when the specimens were inhabiting drifting vegetation.

Water distribution and permeability of zebrafish embryos, Brachydanio rerio

Teleost embryos have not been successfully cryopreserved. To formulate successful cryopreservation protocols, the distribution and cellular permeability to water must be understood. In this paper, the zebrafish (Brachydanio rerio) was used as a model for basic studies of the distribution to permeability to water. These embryos are a complex multi-compartmental system composed of two membrane-limited compartments, a large yolk (surrounded by the yolk syncytial layer) and differentiating blastoderm cells (each surrounded by a plasma membrane). Due to the complexity of this system, a variety of techniques, including magnetic resonance microscopy and electron spin resonance, was used to measure the water in these compartments. Cellular water was distributed unequally in each compartment. At the 6-somite stage, the percent water (V/V) was distributed as follows: total in embryo = 74%, total in yolk = 42%, and total in blastoderm = 82%. A one-compartment model was used to analyze kinetic, osmotic shrinkage data and determine a phenomenological water permeability parameter, Lp, assuming intracellular isosmotic compartments of either 40 or 300 mosm. This analysis revealed that the membrane permeability changed (P < 0.05) during development. During the 75% epiboly to 3-somite stage, the mean membrane permeability remained constant (Lp = 0.022 +/- 0.002 micron x min-1atm-1 [mean +/- S.E.M.] assuming isosmotic is 40 mosm or Lp = 0.049 +/- 0.008 micron x min-1atm-1 assuming isosmotic is 300 mosm). However, at the 6-somite stage, Lp increased twofold (Lp = 0.040 +/- 0.004 micron x min-1atm-1 assuming isosmotic is 40 mosm or Lp = 0.100 +/- 0.017 micron x min-1atm-1 assuming isosmotic is 300 mosm). Therefore, the low permeability of the zebrafish embryo coupled with its large size (and consequent low area to volume ratio) led to a very slow osmotic response that should be considered before formulating cryopreservation protocols.

New approaches for studying the permeability of fish embryos: toward successful cryopreservation

This paper describes some new approaches for understanding the permeability of teleost embryos. The dechorionated zebrafish (Brachydanio rerio) was used as a model for basic studies of water and cryoprotectant permeability. These embryos are composed of two compartments, a large yolk (surrounded by the yolk syncytial layer) and differentiating blastoderm cells. Cellular water was distributed unequally in each compartment. Measurements indicated that the total water in the embryo was 74%, while the total water in the yolk was 42%, and total water in the blastoderm was 82%. The internal isosmotic value for the zebrafish embryo is unknown. However, for one-compartment modeling studies of membrane permeability, the mean Lp (+/- SEM) values were 0.022 +/- 0.002 to 0.049 +/- 0.008 microns x min-1 atm-1 at 40 mOsm (assuming this was one possible internal isosmotic value for the entire embryo) and 0.040 +/- 0.004 to 0.1 +/- 0.017 microns x min-1 atm-1 at 300 mOsm (assuming this was another possible internal isosmotic value for the entire embryo). When three- and six-somite embryos were placed in 1.5 and 2.0 M cryoprotectants (dimethyl sulfoxide and propylene glycol), osmometric measurements of volume changes indicated no cryoprotectant permeation. However, similar measurements with methanol revealed a small volume decrease (ca. 8%) and recovery (ca. 5%) for six-somite embryos in a 2.0 M solution. Magnetic resonance (MR) images of the spatial distribution of three cryoprotectants (dimethyl sulfoxide, propylene glycol, and methanol) demonstrated that only methanol permeated the entire embryo within 15 min. The other cryoprotectants exhibited little or no permeation into the yolk over 2.5 h. The results from MR spectroscopy and cryoprotectant microinjections into the yolk suggested that the yolk syncytial layer plays the critical limiting role for cryoprotectant permeation throughout the embryo.

Chill sensitivity and cryoprotectant permeability of dechorionated zebrafish embryos, Brachydanio rerio

The zebrafish (Brachydanio rerio) was used as a model for basic studies of the chilling sensitivity, permeability and toxicity of cryoprotectants. In both intact and dechorionated embryos, early-stage embryos (1.25, 1.5, 1.75, and 2 h) were more susceptible (P < 0.05) to chilling injury at 0 degrees C than late-stage embryos (50, 75, and 100% epiboly and three-somite stage). Moreover, enzymatic removal of the chorion did not alter (P > 0.05) this pattern of sensitivity to chilling. Eight-hour zebrafish embryos tolerated short-term exposures to temperatures ranging from 4 to 23 degrees C for 3.5 h with no detrimental developmental effects. The permeability of dechorionated embryos to cryoprotectants was examined by measuring the kinetics of volumetric change at various developmental stages (16 cells to six somites or ca. 1.25 to 14 h postfertilization) at 28.5 degrees C. The dechorionated zebrafish embryo is composed of two complex cellular compartments (i.e., a large yolk and the developing blastoderm). From 40 to 100% epiboly, the volumes of yolk and blastoderm remained constant, ca. 82 and 18%, respectively. However, these volumes changed rapidly after epiboly. For example, at the six-somite stage, the yolk composed 61% of the total volume, whereas the blastoderm composed 39%. When three- and six-somite embryos were placed in 1.5 and 2.0 M cryoprotectants (dimethyl sulfoxide and propylene glycol), osmometric measurement of volume changes indicated no permeation of the cryoprotectants. However, some permeation was observed for six-somite embryos immersed in a 2.0 M methanol solution, but not for 3-somite embryos. For up to 30 min at room temperature, these cryoprotectant solutions were toxic to zebrafish embryos; however, 1.5 M glycerol and ethylene glycol solutions were. We conclude that the complex nature of the zebrafish embryo reduces the effectiveness and predictive value of light microscopical measurements for cryoprotectant permeability studies.

Smooth muscle cells in the walls of ovarian follicles in the Japanese quail

The walls of pre-ovulatory follicles of the Japanese quail were examined at the ultrastructural level for the presence of cells displaying the typical morphological features of smooth muscle cells. These characteristics were found in the cells of the chordae, the tunica albuginea, and the theca externa. Small, elongated cells, containing microfilaments, were observed in the theca of prelampbrush follicles localized in the ovarian cortex. These thecal cells were considered as the putative precursors of the thecal smooth muscle cells of the pre-ovulatory follicle. The difference between the smooth muscle cells of the pre-ovulatory follicle and those in the wall of the most recent post-ovulatory follicle is the contracted state of the latter, which is most evident in the cells of the theca externa. It can be concluded that the cells of the theca externa are smooth muscle cells which are mainly contracted during the ovulatory process. A comparison was made with other vertebrate species.

Localization of smooth-muscle markers in the ovaries of some ectothermic vertebrates

In the present study, we have localized desmin and alpha-smooth-muscle actin in the ovaries of the zebrafish, the axolotl, and the red-eared turtle, using the unlabelled antibody peroxidase-antiperoxidase technique. In the axolotl ovary both smooth-muscle markers were demonstrated in cord-like structures, extended along ovarian blood vessels, and in some inner ovarian epithelium cells. In the ovaries of the teleost, smooth-muscle-like cells are detected in a suspensory apparatus formed by venous cords, the tunica albuginea, and the coat around the ovarian artery. Also, in the turtle ovary, smooth-muscle-like cells were found in a suspensory apparatus formed by chordae, the tunica albuginea, and the theca externa of the ovarian follicles. At the present time, the prevailing hypothesis is that, in addition to a role in the mechanical support, the smooth-muscle-like cells in the ovaries of these vertebrates seem to be important with respect to ovarian contractile processes.

Ultrastructural aspects of oogenesis and oocyte growth in fish and amphibians

Oogenesis, the early events of primary oocyte growth (meiotic arrest, synapsis, ribosomal gene duplication), and folliculogenesis can be seen to particular advantage in the germinal ridge of the syngnathan ovary. After budding off the germinal ridge (a compartment of the luminal epithelium), nascent follicles then enter into a linear array of developing follicles within which temporal and stage-specific events can be correlated with spatial distribution. Prominent features of the later phase of primary oocyte growth include intense transcriptional activity and the formation and subsequent dispersal of the Balbiani vitelline body (mitochondrial cloud) concomitant with an increase in cytoplasmic organelles and volume. Further oocyte growth is characterized by a period of cortical alveolus (in teleosts) or cortical granule (in anurans) formation, in which Golgi elements play a predominant role, and finally vitellogenesis. The latter process, which is responsible for the preponderance of oocyte growth, includes the hepatic synthesis and secretion of vitellogenin (VTG), the uptake of VTG from the bloodstream into the oocyte by receptor-mediated endocytosis, and the transport of VTG via endosomes and multivesicular bodies to forming yolk platelets. In the process, VTG is proteolytically cleaved into the yolk proteins, which assume either a monoclinic (in cyclostomes) or orthorhombic (in teleosts and amphibians) crystalline array. Other structures associated with the growing oocyte are also briefly discussed, including nuage, the vitelline envelope, intercellular junctions between the oocyte and overlying follicle cells, pigment, intramitochondrial crystals in ranidae, and annulate lamellae.